Preparation, Structure, and Properties of Polystyrene-Microsphere-Reinforced PEG-Based Hydrogels

Anti-marine biofouling adhesion performance and mechanism of PDMS fouling-release coating containing PS-PEG hydrogel

Polystyrene microspheres compounded with polyethylene glycol-based hydrogel (PS-PEG)/polydimethylsiloxane (PDMS) coatings were prepared using the physical blending method. The chemical structure, surface and interface properties, interlayer adhesion, and tensile properties were tested in this paper. Furthermore, the antifouling performance was evaluated through bovine serum albumin fluorescent protein adsorption testing, marine bacteria adhesion testing, and benthic diatom adhesion testing. The results showed that the coating performance was best when 20 wt% PS-PEG hydrogel was added. Its surface energy was only 19.21 mJ/m2, the maximum breaking strength was 1.24 MPa, the maximum elongation rate was 675 %, the elastic modulus was 2.53 MPa, and the anti-stripping rate was 100 %. In addition, the coating with added 20 wt% PS-PEG hydrogel bacterial adherence rate was 5.36 % and 2.45 % after rinsing and washing, respectively, and the removal rate was 54.29 %. In the benthic diatom adhesion test, the chlorophyll concentration a-value was only 0.0017 mg/L after washing with added 20 wt% hydrogel, and the protein desorption rate was 84.19 % higher than PDMS in the fluorescent protein adsorption test. This coating has the 'low adhesion' and 'desorption' characteristics in the three growth stages of biofouling. Meanwhile, the low surface energy of the silicone is stable, and the hydrogel also dynamically migrates to the surface to gradually form a hydration layer, both are synergistic. When 20 wt% PS-PEG hydrogel was added, the coating demonstrated excellent antifouling performance due to its high hydration layer, low surface energy, high elasticity, and high interlayer adhesion. This research is expected to contribute to the practical applications of hydrogel coatings in marine antifouling.

Laser-Generated Scholte Waves in Floating Microparticles

This study aims to demonstrate the generation and detection of Scholte waves inside polystyrene microparticles. This was proven using both experimental analysis and COMSOL simulation. Microspheres of different sizes were excited optically with a pulsed laser (532 nm), and the acoustic signals were detected using a transducer (40 MHz). On analyzing the laser-generated ultrasound signals, the results obtained experimentally and from COMSOL are in close agreement both in the time and frequency domain. A simplified analysis of Scholte wave generation by laser irradiation for homogeneous, isotropic microspheres is presented. The theoretical wave velocity of the Scholte wave was calculated and found close to our experimental results. A representation of pressure wave motion showing the Scholte wave generation is presented at different times.

Swelling Behaviour of Polystyrene Microsphere Enhanced PEG-Based Hydrogels in Seawater and Evolution Mechanism of Their Three-Dimensional Network Microstructure

To understand the microstructure evolution of hydrogels swollen in seawater, freeze-drying technology was used to fix and preserve the swollen three-dimensional microstructure. By this method, we revealed the swelling behavior of hydrogels in seawater, and elucidated the mechanism of the swelling process. Meanwhile, we also used Fourier-transform infrared spectroscopy; laser confocal microscopy; field emission scanning electron microscopy, and swelling performance tests to research the structure and properties of PS-PEG hydrogels, before and after seawater swelling, and analyzed the structure and properties of PEG-based hydrogels with different contents of polystyrene microspheres. Results showed that PS-PEG hydrogels went through three stages during the swelling process, namely ‘wetting-rapid swelling-swelling equilibrium’. Due to the capillary effect and hydration effect, the surface area would initially grow tiny pores, and enter the interior in a free penetration manner. Finally, it formed a stable structure, and this process varied with different content of polystyrene microspheres. In addition, with the increase of polystyrene microsphere content, the roughness of the hydrogel before swelling would increase, but decrease after swelling. Appropriate acquisition of polystyrene microspheres could enhance the three-dimensional network structure of PEG-based hydrogels, with a lower swelling degree than hydrogels without polystyrene microspheres.

3D Interlayer Slidable Multilayer Nano-Graphene Oxide Acrylate Crosslinked Tough Hydrogel

The design of three-dimensional crosslinked units with a spatial structure is of great significance for improving the mechanical properties of hydrogels. However, almost all the nanocomposites incorporated in hydrogels were defined as rigid nanofillers without further discussion on the potential contribution from the spatial structure change. In this work, the 3D nano chemical crosslinker multilayer graphene oxide acrylate (mGOa) was developed as a pressure-responsive crosslinker to achieve both low elastic modulus and high compression stress by synergizing more polymer chains against the loading force through interlayer sliding. Results showed that the hydrogel crosslinked by only 2 mg/mL mGOa nano chemical crosslinker in the poly(2-hydroxyethyl methacrylate-co-acrylamide) hydrogel (molar ratio: 1:1) can effectively enhance the mechanical strength up to 14.1 ± 2.1 MPa at a high compressive strain (90.6%) with an elastic modulus of less than 0.03 MPa at the initial 5% compression, whereas the hydrogel crosslinked by methacrylated single-layer graphene oxide (sGOa) or a small-molecule chemical crosslinker, N,N'-methylene bisacrylamide, can only reach 2.3 ± 0.8 MPa and 1.4 ± 0.4 MPa, respectively. In addition, the instantaneous modulus of the mGOa crosslinked hydrogel rapidly increased to the peak value with the increase of strain. The repeated compression test of HcA-mGOa hydrogels showed the responsive increase of the modulus, which was promoted by the synergism of polymer chains under compression. This indicated that the interlayer sliding of mGOa is the key contributor to mechanical strength enhancement, which provides a new rationale to design tough hydrogels.